using MoonTools.ECS;
using Nerfed.Runtime.Scene.Streaming;
using System;

namespace Nerfed.Runtime.Resources;

/// <summary>
/// A typical rendering preparation system that natively resolves and requests
/// asynchronous background loading for its own required assets, removing the 
/// need for a monolithic generic AssetStreaming manager.
/// </summary>
public class SampleRenderSystem : MoonTools.ECS.System
{
    private readonly Filter _meshVisualsFilter;

    public SampleRenderSystem(World world) : base(world) {
        _meshVisualsFilter = FilterBuilder
            .Include<SampleMeshVisualComponent>()
            // Always ignore chunk entities technically "unloading" from RAM
            .Exclude<ChunkUnloadPendingTag>()
            .Build();
    }

    public override void Update(TimeSpan delta) {
        foreach(Entity entity in _meshVisualsFilter.Entities) {
            SampleMeshVisualComponent visualComp = Get<SampleMeshVisualComponent>(entity);

            // 1. Resolve State
            ResourceState vertState = ResourceManager.GetState(visualComp.VertexShader.AssetId);
            ResourceState fragState = ResourceManager.GetState(visualComp.FragmentShader.AssetId);

            // 2. Asynchronously request assets if they don't exist in memory yet
            if(vertState == ResourceState.Unloaded) {
                ResourceManager.Retain<Shader>(visualComp.VertexShader.AssetId, "Unknown/Path");
            }
            if(fragState == ResourceState.Unloaded) {
                ResourceManager.Retain<Shader>(visualComp.FragmentShader.AssetId, "Unknown/Path");
            }

            // 3. Prevent rendering logic unless ALL strictly required assets are fully mapped
            bool isReadyToDraw = vertState == ResourceState.Loaded && fragState == ResourceState.Loaded;

            if(isReadyToDraw) {
                // At this exact point, you can safely assume:
                // 1) The background loading threads are 100% finished processing these shaders.
                // 2) The GraphicsDevice can safely extract the native handle.

                // e.g. GraphicsDevice.BindShader(visualComp.VertexShader.AssetId);
                // e.g. GraphicsDevice.DrawPolygons(...);
            }
        }
    }
}